Iron is an essential nutrient for nearly all life forms. It is also a dangerous toxin that must be controlled in biological systems. Proeins that have a high affinity for binding ionic iron or are capable of sequestering it so that it cannot exhibit its harmful effects are produced by virtually all organisms. These same proteins sometimes are used as a defense against parasites and pathogens by depriving them of a nutrient source of iron. The use of the iron-binding proteins transferrin and ferritin as a protection against iron poisoning or defense against pathogens and parasites will be investigated in flies and mosquitoes. It is known the transferrin synthesis is increased by bacterial infection of these insects. This is a part of the insect innate immune system.